Researchers in the musculoskeletal field are increasingly using animal models of human disease, particularly those of tissue injury and repair. In an animal model, a factor believed to be important in the disease process can be administered and the response evaluated and monitored over time. Many assays require sacrifice of the animal in order to extract tissue for analysis;however, longitudinal studies in which changes in a particular animal can be evaluated in vivo and over time are often advantageous. Although both large and small animal disease models currently exist and are readily being developed for various human diseases, the use of small animals (e.g., mouse, rat) has become increasingly preferred for many reasons: 1) the availability of transgenic and knockout animals;2) the ease of procuring large numbers of closely matched animals;and 3) animal cost, handling, housing, and other practical management issues. More importantly, the genome sequences of both the rat and the mouse have been deciphered, giving rise to a wide variety of molecular tools. The University of Pennsylvania has one of the most comprehensive small animal imaging facilities in the world that is staffed by some of the leading scientists in the various imaging modalities. The overall objective of this Small Animal Imaging Core is to develop and utilize a wide range of imaging modalities directed toward problems of musculoskeletal tissue injury and repair. The Specific Aims are: Aim 1: To provide guidance and expertise on the capabilities, advantages, and disadvantages of various imaging modalities for musculoskeletal research through formal educational enrichment programs and oneon- one interactions;Aim 2: To provide facilities and expert collaboration in Small Animal Imaging studies employing MRS/MRI, optical imaging, bioluminescence, PET/SPECT, micro-CT and/or ultrasound;Aim 3: To provide facilities and expert collaboration in Ancillary Facilities including chemistry (for preparation of NMR and optical probes), radiochemistry, molecular biology, image analysis, animal models, and biostatistics;and Aim 4: To provide funding for development of new projects and collaborations, and to develop preliminary and/or feasibility data for investigators. Successful completion of these aims will significantly enhance the environment and the capabilities of researchers at the University of Pennsylvania, leading to novel and innovative approaches to address musculoskeletal disorders and new collaborations between Core faculty who may have not previously included small animal imaging in their musculoskeletal research programs.